1. Field of the Invention
The present invention generally relates to video tape recorders and, more particularly, is directed to a so-called 8-mm video tape recorder in which recorded modes of a pulse-code modulated (PCM) audio data can be identified by checking reproduced signals recorded in the intervals adjacent to the PCM audio data.
2. Description of the Prior Art
In the 8-mm video tape recorder, the video signal is recorded as shown in FIGS. 1 and 2.
As shown in FIG. 1, a frequency-multiplexed signal SV is formed by frequency-multiplexing an FM (frequency-modulated) signal SF, FM-modulated by a video signal SY, a down-converted carrier chrominance signal SC, an FM signal SM, FM-modulated by a sum signal (L+R) of left and right channel audio signals L, R, an FM signal SS, FM-modulated by a difference signal (L-R), and a pilot signal SP used to effect tracking servo in playback mode. This frequency-multiplexed signal SV is recorded on a magnetic tape 2 as one slant video track 2V at every field period as shown in FIG. 2.
In accordance with the technology development of the 8-mm video tape recorder, the PCM audio signal is recorded in a variety of modes, such as shown in FIG. 3.
In "NRML mode", as shown on the second row of FIG. 3, the audio signal is quantized into a digital signal in which a sampling frequency is 31.5 kHz (.apprxeq.2 fh where fh is the horizontal frequency) and one sample is formed of 10 bits. Then, one sample of the digital signal is nonlinearly compressed in data from 10 to 8 bits and converted into a biphase mark signal. This biphase mark signal is recorded on the magnetic tape 2 at a front over-scan interval of the video track 2V over an angular extent of 36 degrees as the track 2A as shown in FIG. 2.
In "L mode", as shown on the third row of FIG. 3, the audio signal is quantized into a digital signal in which a sampling frequency is any of 48 kHz, 44.1 kHz and 32 kHz and one sample is formed of 16 bits. This digital signal is converted in an eight-to-ten conversion fashion and the converted digital signal is then recorded on the magnetic tape 2 at a front over-scan interval of the video track 2V over an angular extent of 41 degrees as the track 2A as shown in FIG. 2.
Further, in "N mode", as shown on the fourth row of FIG. 3, one sample of the quantized digital signal is nonlinearly compressed in data in the form of 16 to 12 bits and then recorded similarly to the L mode.
In actual practice, the recorded signal involves an error correction code, an identifying (ID) code and so on and the transmission rate thereof is presented as shown in FIG. 3. Also, the recorded signal has a pre-amble signal, a post-amble signal and the like added thereto.
The NRML mode is the standard standardized when the 8-mm video tape recorder was introduced and the L and N modes are the standards added or expanded in accordance with the development of the 8-mm video tape recorder technology.
Since the L and N modes are new modes which are added to or expanded in the PCM audio mode of the 8-mm video tape recorder as described above, the existing high-grade video tape recorders can cope with the NRML mode, the L mode and the N mode. However, the NRML mode, the L mode and the N mode are not available in the existing standard type video tape recorders and therefore these standard type video tape recorders have no system to properly identify these modes.